1. Field
One embodiment of the invention relates to an optical disc recording/reproduction apparatus (information recording/reproduction apparatus) for recording, reproducing and erasing information on/from a recordable, reproducible and erasable optical disc by means of a laser beam.
2. Description of the Related Art
An optical disc is widely used as a recording medium suitable for recording, reproducing and erasing (recording repeatedly) information. Various optical discs of different standards have been proposed and are in actual use. According to the recording capacity, these optical discs are classified into CD and DVD. According to the use (data-recording system), the discs are further classified into a play-only type containing prerecorded information (designated ROM), a write-once type capable of recording information once only (designated R), and a rewritable type (recordable/playable or rewritable type) capable of recording and erasing information repeatedly (designated RAM or RW). A projection type display unit using a digital micromirror device (DMD, trademark) as a space demodulation element has been put into practical use.
As the standard and purpose of optical discs have diversified, it has become required that an optical disc recording/reproduction apparatus be capable of recording information on optical discs of two or more standards, reproducing prerecorded information, and erasing recorded information. In addition, it is demanded as an essential condition of an optical disc recording/reproduction apparatus that the apparatus be capable of detecting the standard of an optical disc loaded in the apparatus, even if it is difficult to record and erase information.
Therefore, an optical pickup incorporated in an optical disc information recording/reproduction apparatus is required at least to be capable of capturing reflected light from a track or a string of recording marks peculiar to an optical disc and controlling the tracking and focus of an objective lens (optical pickup) regardless of the standard (type) of the optical disc.
It is disclosed by, for example, Japanese Patent Application Publication (KOKAI) No. 2004-39165 has proposed an optical pickup, which divides reflected light from an optical information recording medium (optical disc) into a portion where a 0th order light and a ±1st order diffraction light are overlapped and a portion where they are not overlapped, enters each portion into an independent optical detecting means, obtains a predetermined signal, and, as a result, provides a good tracking error signal.
However, the diffraction angle of the ±1st order diffraction light of the reflected light from the optical information recording medium described in the above document is different depending on the wavelength of the reflected light, the track pitch of the optical information recording medium, etc.
Therefore, in an optical pickup unit which receives reflected light with several wavelengths or reflected light from track pitches of several types of optical information recording media or data areas, it is impossible to uniquely determine the portion where a 0th order light and a ±1st order diffraction light are overlapped and the portion where they are not overlapped.
In addition, a light-dividing means based on the wavelength and track pitch of one reflected light has difficultly in generating a track error signal normally from reflected light from optical information recording media with different wavelengths or different track pitches.